Two ministers from the last government have raised concerns about the secret meeting between former Garda Commissioner Martin Callinan and Fianna Fáil TD John McGuinness.

Labour leader Brendan Howlin said he was "taken aback" that it took place, while Social Protection Minister Leo Varadkar called it "unusual".

At the January 2014 meeting - revealed by Mr McGuinness in the Dáil last week - Mr Callinan allegedly tried to discredit garda whistleblower Sergeant Maurice McCabe to the then Public Accounts Committee chairman ahead of an appearance by Sgt McCabe.

Mr McGuinness defended his decision not to reveal the meeting to the O'Higgins Commission - which investigated Sgt McCabe's allegations of garda malpractice - saying it wasn't within the inquiry's remit. He also said he would have been accused of "tampering" with the investigation if he had.

Mr Howlin said he would have expected the meeting to have been revealed earlier and brought to the attention of Mr O'Higgins. Asked if the meeting influenced his statement of confidence in Mr Callinan at the time, Mr Howlin replied: "Yes it would."

He said the alleged attempt to undermine Sgt McCabe was "profoundly worrying and it certainly would have coloured all of our views on the conduct of the most senior garda at the time. We obviously have to hear what exactly was said and former Commissioner Callinan, no doubt, will be in a position to do that".

Mr Varadkar said it would have been "helpful" if Mr McGuinness had told the O'Higgins Commission about the meeting. He said it was up to Mr Callinan to decide whether or not to address the controversy.

Mr Varadkar, who previously described the whistleblower as "distinguished", said this position had been "vindicated". He added that he "never believed" stories circulated about Sgt McCabe which, in his view, were "being put about to undermine his credibility".

Last night, one Fianna Fáil source described Mr McGuinness's decision to reveal the meeting now as "baffling", adding: "I'm struggling to figure out what purpose it serves."

Another party member said Mr McGuinness should have brought the matter to the O'Higgins Inquiry. Mr McGuinness said he had "no comment".

He previously said he had an obligation to reveal the meeting now because of recent attempts to discredit Sgt McCabe.